This invention relates generally to vehicle tire monitoring systems, and more particularly relates to a system for transmitting power to an aircraft tire pressure sensor from a low frequency (LF) RFID reader for transmitting data between an aircraft tire pressure sensor and the control unit. The invention pertains more specifically to a communication link between a tire pressure sensor on a wheel rim and control electronics connected to a wheel hub or a hand held reader/transponder, particularly adapted to use on aircraft.
It is useful in an airplane to monitor information relating to each tire, such as pressure or temperature information, for example, and provide this information in the cockpit or to flight line tire service personnel. It is necessary to communicate this information from the wheel rim to electronics located on the wheel axle or within the hand held reader/transponder.
One known tire pressure system uses a pair of transformer coils to communicate between a primary and secondary coil in the wheel axle. These transformers are coaxial and face each other. A length of wire connected to the secondary of the transformer pair connects directly with the tire pressure sensor that is located on the periphery of the wheel rim. However, it would be desirable to provide an aircraft tire pressure link for electromagnetically coupling a magnetic field between a wheel hub coil and a tire pressure sensor coil that does not use unreliable electrical connections and does not use wires that are otherwise prone to breakage in the harsh environment of the airplane wheel. It is thus desirable to provide a non-contact method of communication between an airplane wheel hub and a tire pressure sensor located on the rim of the wheel that does not require electrical connections or a length of wire to communicate between the wheel hub and the tire pressure sensor. More specifically, it would be desirable to provide wireless communication between an airplane wheel hub or a hand held reader/transponder and a tire pressure sensing transponder located on the rim of the wheel up to six inches away from the wheel hub or transponder antenna.
RFID antenna concepts are widely known in the form of air-core coils and ferrite rod solenoids. This technology is represented in, e.g., the RFID Handbook, or U.S. Pat. No. 6,839,035 (Addonisio) wherein a magnetic coupling range extension is achieved with a tuned resonant interposer coil. Also known is US 2008/0042850 A1, wherein a hybrid RFID tag includes circuitry that can be positioned within an open area defined by a first antenna, and includes a battery that can be positioned within another area defined by the first antenna.
Much of the prior art applies to high frequency RFID where frequencies are too high to effectively direct flux through highly permeable media (such as high nickel alloy metals) over any useful distance. Low frequency (LF) RFID transponder antennas have typically required that the antenna coils be directly exposed to the magnetic field per Faraday's Law wherein EMF is proportional to the area of the coil that is within the changing magnetic field. This traditional field coupled coil practice results in large area coils to achieve magnetically coupled RFID communication over extended distances.
It would be desirable to provide a low frequency RFID transponder system for use in sensor package systems, such as in a tire pressure sensor system or temperature sensor system, for example, and to allow the use of a low frequency RFID antenna in sensor package systems that have become industry standard prior to RFID technology, without altering the legacy form factor of those sensors. It would be desirable to design the magnetic properties of such sensor package systems to manage magnetic flux path impedances to concentrate and direct magnetic flux through an internal coil of a transponder antenna, and then allow the flux to return from the external surface of the transponder antenna coil to the reader antenna.
The need exists for embedding RFID antennas within sensor packages which would otherwise not be suited for use in an exposed area of an aircraft landing gear, due to the size, shape, and environmental concerns that apply to antenna coils with large cross-sections.
It also would be desirable to provide a range extension for a low frequency RFID transponder sensor system by forming the shape of a magnetic field from a reader antenna of such a low frequency RFID transponder sensor system, and establishing an efficient field pattern pairing between reader and transponder antenna flux paths. It further would be desirable to utilize and optimize the flux directing possibilities that exist in the LF RFID frequency band.
It would also be desirable to provide a low frequency RFID sensor transponder system in which a sensor transponder assembly enclosure is configured to use environmental and structural metal features to also serve a magnetic function which effectively increases the flux collecting area of the coil, permitting the use of smaller sensor transponder coils. It would be desirable for the magnetic flux from an LF RFID transponder antenna to be collected by a magnetically permeable metal on the exterior of the sensor enclosure, and then concentrated and directed by a portion of the same magnetically permeable metal of the sensor enclosure through the center of an electrical wire coil, even when the coil is located within the sensor enclosure. The present invention meets these and other needs.